Support JUMP_BACKWARD

This is not very useful right now.
It would need either FOR_ITER[_RANGE, etc.] or POP_JUMP_IF_XXX.

Author: gvanrossum

Python/ceval.c

@@ -2767,6 +2767,13 @@ _PyUopExecute(_PyExecutorObject *executor, _PyInterpreterFrame *frame, PyObject
 #define ENABLE_SPECIALIZATION 0
 #include "executor_cases.c.h"
 
+            case JUMP_TO_TOP:
+            {
+                pc = 0;
+                CHECK_EVAL_BREAKER();
+                break;
+            }
+
             case SAVE_IP:
             {
                 frame->prev_instr = ip_offset + oparg;

Python/opcode_metadata.h

@@ -426,6 +426,18 @@ translate_bytecode_to_trace(
             oparg = (oparg & 0xffffff00) | executor->vm_data.oparg;
         }
         switch (opcode) {
+            case JUMP_BACKWARD:
+            {
+                if (instr + 2 - oparg == initial_instr
+                    && trace_length + 3 <= max_length)
+                {
+                    ADD_TO_TRACE(JUMP_TO_TOP, 0);
+                }
+                else {
+                    DPRINTF(2, "JUMP_BACKWARD not to top ends trace\n");
+                }
+                goto done;
+            }
             default:
             {
                 const struct opcode_macro_expansion *expansion = &_PyOpcode_macro_expansion[opcode];

Python/optimizer.c

@@ -1344,6 +1344,7 @@ def add(name: str) -> None:
             counter += 1
         add("EXIT_TRACE")
         add("SAVE_IP")
+        add("JUMP_TO_TOP")
         for instr in self.instrs.values():
             if instr.kind == "op" and instr.is_viable_uop():
                 add(instr.name)